Expert: Bruce E. Johnson - 8/12/2010

Question
Is it better to encapsulate the air in a 4 foot crawl space
or use an air conditioning system like Atmox or EZ Breathe?
Is insulating the perimeter block wall by injecting foam in the cores more effective than placing insulation in the
spaces between the floor joists?

Answer
Hik Norm, it depends on the humidity issues in your area but the key to good crawl space conditioning is #1 having a good vapor barrier on the ground. Minimum 6 mil visqueen with all the seams taped and sealed.  Moisture coming up from the ground makes up a good portion of crawlspace humidity.  #2 having good air flow:  Moving air keeps the area fresh but also pulls moist air through the crawlspace during wet weather.  This is not necessarily a bad thing.  Being too dry can be a problem also.  That's why I like the concept of the Atmox type of system.  It regulates the humidity and keeps it within the proper levels.  But good block vents equally spaced around a house have been around for years and seem to work decently also.  One 8"X 16" vent per 100 square feet of the house's footprint is generally the norm. So if your house is a thousand sq. feet you should have 10 vents equally spaced around the perimeter.  As for insulation?  A closed air space that is being conditioned by mechanical means should have the exterior block foundation insulated.  Core-fil provides somewhere around an R-16 in 8" masonry.  If you have a ventilated foundation then under joist insulation is recommended with the vapor barrier facing down.  I hope this information helps please feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com